The group urges that experiments that produce potential pandemic strains “should be curtailed until there has been a quantitative, objective and credible assessment” of the risks, potential benefits, and alternatives. They call for a process akin to Asilomar, a 1975 summit that came up with guidelines for recombinant DNA technology.

Concerns about “gain-of-function” experiments with influenza erupted in 2011 after two teams genetically tweaked the H5N1 avian flu virus, which has killed some people, to make it more transmissible in mammals. Supporters of such studies say knowing which mutations help the virus spread in humans is useful for surveillance efforts and developing pandemic vaccines. After much debate and a moratorium on the H5N1 studies, a consensus emerged that the experiments could resume with new safeguards.

The 18-and-counting signatories include scientists who have stridently opposed the gain-of-function experiments, including virologist Michael Osterholm of the University of Minnesota and Harvard epidemiologist Marc Lipsitch. Others include Nobelist Richard Roberts of New England Biolabs, former Harvard School of Public Health Dean Barry Bloom, and activist Edward Hammond of the Third World Network.